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Old 04-21-2011, 01:18 PM   #1
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Wiring power to detached garage, more questions


Okay, so what I have available at HD/Lowes that would work for a subpanel doesn't appear to include anything heavier than 2 gage that has 4 conductors... There is 2-2-2-4 aluminum mobile home feeder. I'm wanting to put in a 100 amp in the garage. There is available 2/0-2/0-2/0 but that would leave me without a ground conductor.

Would it be allowable to use 2/0-2/0-2/0 aluminum SEU and run another conductor seperately in the conduit for ground?

I can get 2/0 copper individual THHN, but that would cost more than using RMC all the way and I believe if I used RMC I'm allowed to use the conduit as the ground conductor, but I'd rather use PVC conduit (sch. 80 risers, sch.40 in the trench)

I'm strongly leaning towards doing the 200 amp service upgrade and entrance move at the same time, so this will be a 100 amp sub running directly off a 200 amp main.

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Old 04-21-2011, 01:28 PM   #2
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Wiring power to detached garage, more questions


You can breaker the #2Al at 90A which should meet your needs.

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Old 04-21-2011, 01:43 PM   #3
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Would it be allowable to use 2/0-2/0-2/0 aluminum SEU and run another conductor seperately in the conduit for ground?
Yes you can
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Old 04-21-2011, 04:26 PM   #4
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NO you can't!!

save it is in a conduit and then it would be much cheaper to run all THHN/THWN
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Old 04-21-2011, 04:37 PM   #5
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NO you can't!!
Explain why not.
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Old 04-21-2011, 04:45 PM   #6
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Well, 2/0-2/0-2/0 SEU is $1.96 per foot while 2" RMT is $48.96 for 10' at HD. On the other hand I can go to an electric supply and get 2/0 XHHW at $.96/ft. Even if I put in a 2/0 copper THHN from HD at $2.50 to ground with the SEU it comes out cheaper per foot than the RMT conduit.
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Old 04-21-2011, 05:01 PM   #7
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The question was
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Would it be allowable to use 2/0-2/0-2/0 aluminum SEU and run another conductor seperately in the conduit for ground?
It was not about cost.
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Old 04-21-2011, 05:34 PM   #8
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Wiring power to detached garage, more questions


I would know, it was my question!

Anyway, the question was started because as near as I could tell from what's available at HD, 2/0-2/0-2/0 SEU in PVC conduit with another cable for a ground conductor seems to be my most cost effective option. I did look at using rigid metal conduit since I read that code allows metal conduit to be used as your ground conductor, but the price of the rigid metal conduit really drove the cost up a lot more.

I know of one electrical supply store nearby, and they have 2/0 aluminum individual conductors so that's an option at $.96 per foot which is more than the 3 conductor cable at HD and probably more than 3 conductor + 1 conductor ground.

At this point, I need to figure out conduit... The electrical supply store I know of nearby does not carry schedule 80 PVC, so that is a problem that's proving harder to overcome than I expected. I can keep looking, but is there any way to make a connection between rigid metal conduit and schedule 40 PVC? If so then I could just use the rigid for risers.
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Old 04-21-2011, 05:45 PM   #9
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Wiring power to detached garage, more questions


Willk
I was answering Sat Night Cowboy. You do not need SCh80 conduit for this installation. Sch40 would be fine. I can't help with making the connections. Let me check that out.
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Old 04-21-2011, 06:29 PM   #10
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Sch 40 is ok for the run and riser. Check this out 222.
http://books.google.com/books?id=xGt...%20nec&f=false

Last edited by wareagle; 04-21-2011 at 06:32 PM.
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Old 04-21-2011, 09:00 PM   #11
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Wiring power to detached garage, more questions


Unfortunately, I've run into this problem with my inspector already on a previous aspect of the project. On a surface mounted run in the utility room for a dedicated circuit for the sink pump, I used schedule 40 PVC. This was at about 40" above the ground, around a corner behind the utility sink. A run of about 8' total. He rejected the PVC because it is not rated for mechanical damage. I guess for all those times a set of swinging blades comes flying out of the sink drain. I replaced it with EMT and he was fine.

Now mind you, I'll talk to him because schedule 80 gives me something I can actually point to, but I have to find somewhere I can buy it first. I haven't had the opportunity to talk to him since I got it in my head to get this project started, which pretty well happenned today and AHJ is overdue for retirement, so he's only working mornings and has 2 days off or something like that - being easter, he wasn't in today.

And if I really wanted to argue the point with him (frankly, I don't unless I'm really backed into a corner) I'd have a problem because according to Carlon's web site, schedule 40 underground runs with schedule 80 risers is common because they say that their schedule 40 is not rated for the mechanical damage requirement of the electrical code. Carlon discusses it quite a bit in an FAQ because questions come up about the sharp edge from the transition between thick to thicker wall and so on.

I think my understanding is that EMT is not rated at all for burial, only intermediate and rigid metal.

Unfortunately I'm finding it a little hard to locate a supplier of schedule 80, which says that maybe some AHJ are accepting schedule 40 in the area or maybe most people are just going to rigid metal tube for underground runs. I'm assuming that schedule 80 PVC is going to be more than schedule 40 but much much less than rigid metal?
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Old 04-22-2011, 07:49 AM   #12
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Wiring power to detached garage, more questions


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Originally Posted by WillK View Post
Now mind you, I'll talk to him because schedule 80 gives me something I can actually point to, but I have to find somewhere I can buy it first.
Home Depot carries Sch 80 PVC conduit in several sizes.
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Old 04-22-2011, 08:51 PM   #13
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Wiring power to detached garage, more questions


Hmm... well, I haven't seen it, not locally at least. Or should I be looking for schedule 80 PVC in plumbing? I am certain they only have schedule 40 PVC electrical conduit.
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Old 04-22-2011, 10:36 PM   #14
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Wiring power to detached garage, more questions


I'd just go to an electrical supply store. This sort of stuff is kind of above & beyond the norm for HD/Lowe's in my opinion.
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Old 04-23-2011, 08:01 AM   #15
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Wiring power to detached garage, more questions


Wareagle, SEU cannot be used underground.

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